This study was initiated to determine whether the effects of hexachlorobenzene (HCB) on drug metabolism and on toxicity are related to contamination by chlorinated dibenzodioxins or other impurities, or whether HCB acts through a mechanism similar to the dioxins. This work was extended to determine whether the cytochrome(s) P-450 induced by HCB were identical to that induced by 3-methylcholanthrene (3-MC) and 2,3,7,8-tetrachlorodibenzodioxin (TCDD).